Higher symbol (baud) rates are likely to be implemented in next-generation networks to provide data rates in excess of 100 Gigabits per second (Gbps) over relatively long distances, e.g., 500 kilometers or more. Some network components may be unable to support such high symbol rates without introducing significant distortion into the signal. One form of signal distortion is inter-symbol interference (ISI), which occurs when leading symbols interfere with trailing symbols. ISI typically results when a signal is communicated over a dispersive channel, which causes individual pulses of symbols in the signal to appear smeared and/or broadened upon reception. The source of ISI is largely medium dependent. In wireless channels, ISI is primarily attributable to multipath propagation, which occurs when the wireless signal traverses multiple paths between the transmitter and receiver. In optical channels, ISI is primarily attributable to chromatic dispersion, which occurs when light of different wavelengths travels through the fiber at different speeds. Additionally, ISI may be attributable to the band-limited nature of optical front-ends and various network elements (e.g., wavelength selective switches (WSS). Excessive ISI can introduce errors into signal decoding at the receiver. Therefore, techniques for reducing ISI in high baud rate networks are desired.
Although ISI is an additive impairment introduced by the channel, impairment may also occur in the form of phase noise. For systems, that have a high data rate the phase noise may be correlated between two or more consecutive symbols. Techniques that help in mitigation of phase noise with memory are therefore also desired for high baud rate systems.